Cpl. John Leatherby (Ted Avery), an American soldier stationed in West Berlin, is kidnapped after escorting his German girlfriend to her home. The Soviets deny involvement in the kidnapping through their intermediary Col. Lodejinski, who is secretly an American and British intelligence asset. Charles Leatherby, the corporal's father and a Toledo industrialist, attempts to expedite his son's retrieval by leveraging his ties to the Eisenhower administration and prominent senators. The elder Leatherby flies to West Berlin and attempts to bully State Department and military officials into quickly retrieving his son, demanding that they offer the Soviets a monetary bribe. Meanwhile, Lt. Col. Steve Van Dyke (Gregory Peck), the eccentric provost marshal for the American sector, is contacted by his old flame and East German source "Hoffy" Hoffmeir (Anita Björk). Hoffmeir implies that Cpl. Leatherby has been kidnapped by the Soviets or East Germans, who intend to exchange him for two West Berliners, Herr and Frau Schindler. Lacking viable alternatives, Van Dyke allows Hoffmeir to facilitate the trade.
After a tense meeting with Leatherby, Van Dyke invites him to dinner at the Katacombe restaurant, ostensibly to discuss the proposed exchange. Instead, Van Dyke attempts to make Leatherby understand the human cost of the trade by revealing the restaurant's piano player and her husband, who was blinded by the Nazis, as the Schindlers. While visibly disturbed by the prospect of sending the elderly couple to their deaths, Leatherby insists that the exchange proceed. Van Dyke has the couple arrested, but they attempt suicide by strychnine poisoning and are transported to an American military hospital. There, the piano player reveals herself as Rachel Cameron (Jill Esmond), an English expatriate and MI6 asset, and her husband as General Gerd von Kratzenow (Anton Farber), an anti-Nazi conspirator who had been jailed and tortured by the Nazi regime. Cameron reveals that she and her husband, now living under the name Schindler, are being pursued not by the Soviets themselves but by ex-Nazi agents responsible for von Kratzenow's torture, who now serve the Eastern Bloc. Separately, Van Dyke prepares to exfiltrate Col. Lodejinski and his family to the United States, but Lodejinski's American ties are leaked and he commits suicide after killing his entire family.
Van Dyke learns from a colleague in military intelligence that his source, Hoffmeir, is an impostor Eastern Bloc asset herself. Van Dyke suspects that Hoffmeir is responsible for exposing Lodejinski as an American asset, but allows her to proceed with arrangements for the agreed-upon exchange. By claiming to Hoffmeir that von Kratzenow succumbed to the strychnine, Van Dyke sets the stage for a one-to-one trade of Cpl. Leatherby for Cameron. Van Dyke arranges for an ambulance to cross into West Berlin to effect the exchange. He is warned by State Department official Hobart (Max Showalter) that the United States government will disavow his actions if they prove unsuccessful. To facilitate the exchange without endangering American or British assets, as Cpl. Leatherby is removed from the ambulance, Van Dyke knocks Hoffmeir unconscious and presents her as Cameron. American military police force the ambulance to return to East Berlin before its escort can confirm the patient's identity. Having secured Cpl. Leatherby's return, Van Dyke is warmly congratulated by the senior Leatherby, who appears humbled by the experience. Cpl. Leatherby's repatriation is represented by the American media as a signal of warming relations with the Soviet Union.